Pumps have long been used to introduce and disperse air and other fluid media into a pumped liquid. For instance, pumps have been used for the production of an air and water mixture. The air so introduced facilitates the removal of oil and other pollutants including solid particles which tend to separate out as a surface scum with the introduction of air and liquid to the tank. The aerated liquid produced by the pump of course may be used for other purposes.
It is known in the art that aeration of liquids is a useful procedure relied upon in pollution control operations. A known procedure, by way of example, is the aeration of sewage contained in a holding tank, with such tending to produce separation of pollutants in the liquid in the tank either as a scum or as sediment. A convenient approach for introducing such air would be to introduce air in the desired quantity to the suction or intake side of the pump during a pumping operation, with the pump then tending to produce a mixture of air and liquid which is expelled from the pump. The problem with this approach is that the addition of significant quantities of air to the intake of the pump will cause the pump to lose outlet pressure and stop pumping. Pump performance is also affected. U.S. Pat. No. 3,663,117 to Warren discloses a so-called aeration pump, wherein air is introduced against the front side of a pump impeller in a centrifugal pump, with the impeller vanes therein then producing mixing of the air and liquid pumped to produce aeration of the liquid. Such a system, because of the relatively high pressure condition existing adjacent the periphery of the impeller, requires a source of air at superatmospheric pressure to be supplied to the pump chamber. In another system, the liquid discharged from a pump is supplied to an air saturation tank. This tank is also supplied air from a compressed air source, and the air and liquid are then mixed in the tank. The need for an air compressor and other equipment adds to the complexity and expense of any system requiring a source of pressurized air. All of these methods also only achieve a limited dispersion of the air into the water because of the limited mixing that can occur as they are passed through the pump.
It is also possible to utilize a pump to disperse other fluid, such as gases other than air or another liquid, into the pumpage. U.S. Pat. No. 4,744,722 to Sampi et al., for instance, describes a pump system for introducing liquid or gas into pulp stock. More generally, U.S. Pat. No. 3,948,492 to Hege discloses a system for mixing a second material into a first fluid material by use of a centrifugal impeller.
When introducing a second material into a pumped flow, one of the primary goals is obtaining a good dispersion of the introduced material into the pumped flow. With conventional systems, good dispersion is difficult to achieve because the added material is injected directly into the stream of the pumped liquid and is therefore rapidly carried out of the pump. Prior art systems often attempt to compensate for this deficiency by introducing the second material from a plurality of points. This method of addressing the problem, however, is of limited success and adds significantly to the complexity of the pump and injection system.
It is therefore an object of the present invention to provide a method and apparatus for finely dispersing a fluid material in a pumped liquid.
It is another object of this invention is to provide an improved method and apparatus for conditioning a liquid by the introduction of air into the liquid, with the air on introduction becoming dissolved in the liquid or entrained as a fine dispersion therein.
Another general object is to provide an improved sewage treatment method which utilizes recycled sewage conditioned with air in the treatment process.
Yet a further object is to provide an improved pump operable to produce a mixture of a pumped liquid and a second fluid.
A more specific object is the provision of such a pump, which employs air introduced into a seal chamber in the pump, and structure within the seal chamber producing an air liquid mixture which under the action of the pump impeller moves to the periphery of the impeller and then to the pump discharge.